Wafer processing film

ABSTRACT

This invention provides a wafer processing film comprising a base film having a Shore D hardness of 40 or less and an adhesive layer disposed on one surface of the base film. In grinding the surfaces of wafers such as silicon and similar wafers, breakage can be prevented by affixing the wafers to the adhesive layer of the processing film and then grinding them.

This is a continuation division of application Ser. No. 823,492, filedJan. 16, 1986, as PCT JP55/00285 on May 23, 1985, published asWO85/05734, on Dec. 19, 1985, now U.S. Pat. No. 4,853,286 .

DESCRIPTION

1. Technical Field

This invention relates to a film which is used in the grinding of waferssuch as silicon and other wafers so as to prevent their breakage.

2. Background Art

Wafers for use in the fabrication of semiconductor chips include siliconwafers, gallium arsenide wafers and similar wafers. Among others,silicon wafers are being widely used. For example, silicon wafers areproduced by cutting a high-purity 5 single-crystal silicon ingot into:slices having a thickness of the order of 500 to 1000 μm. In recentyears, these wafers are tending to become thinner as the size of chipsis reduced and the production scale of chips is enlarged. Moreover, thediameter of these wafers is passing from the conventional value of 3-4inches to 5-8 inches.

Silicon wafers are inherently fragile. In addition, silicon wafershaving integrated circuits formed in their surface are easily broken,even under the action of slight external forces, because of theirsurface roughness. This disadvantage constitutes a serious obstacle topost-processing operations such as back surface grinding.

As a method for preventing silicon wafers from being broken duringsurface grinding there has conventionally been employed the method inwhich, prior to surface grinding, silicon wafers are coated withparaffin, resist ink or the like so as to compensate for their surfaceroughness and to distribute properly the external forces exertedthereon. However, this method involves the step of drying andsolidifying paraffin or the like after its application to a wafersurface and the step of washing off the paraffin or the like from theground wafer with a solvent under the application of heat, thusrequiring complicated operation. In addition, this prior art method isstill unable to prevent wafer breakage in the grinding of wafers havinga diameter of 5 inches or greater, which has constituted a seriousobstacle to the enhancement of productivity. Moreover, the use ofparaffin or the like involves the problem of contamination of wafersurfaces. Accordingly, it has been strongly desired to develop a methodfor the prevention of wafer breakage which can replace the applicationof paraffin or the like.

As a method for the prevention of wafer breakage which can replace theapplication of paraffin or the like, one in which a processing filmhaving an adhesive layer is affixed to a wafer surface has beeninvestigated. However, this method has been unable to prevent waferbreakage perfectly. Moreover, it has been found that, where such aprocessing film is used, airborne dust may adhere to the adhesive layerduring the manufacture, transport or storage of the film. If this dustis transferred and attached to the wafer surface, deterioration of thesemiconductor due to wafer corrosion or the like and, further,malfunction or other problems may result. In other words, where such aprocessing film is used, the dust attached to the wafer surface cannotbe satisfactorily removed simply by cleaning the processed wafer in theconventional manner. Because of these problems, no practical method forpreventing wafer breakage by use of a processing film has been developedas yet.

DISCLOSURE OF THE INVENTION

In view of the above-described problems, the present inventors conductedresearch concerning the method of preventing the breakage of wafersbeing processed and have found that the breakage of wafers can beprevented by affixing a processing film having a specific hardness to awafer surface with an adhesive layer interposed therebetween, so as tocompensate for the roughness of the wafer surface and to distributeproperly the external forces exerted thereon during processing. Theyhave also found that, by laminating an auxiliary film having a specifichardness to the opposite surface of this processing film to that havingan adhesive layer disposed thereon, its workability in affixing theprocessing film to a wafer and separating it from the processed wafercan be greatly improved without impairing its effect of preventing waferbreakage. Furthermore, they have found that the above-described removalof dust can be easily achieved by properly choosing the composition ofthe adhesive substance constituting the adhesive layer. The presentinvention has been completed on the basis of these findings.

It is an object of the present invention to provide a wafer processingfilm which, when used in the surface grinding of wafers and, inparticular, of silicon wafers, can prevent their breakage perfectly.

It is another object of the present invention to provide a waferprocessing film which is easy to handle and which can improveproductivity in wafer processing operations including cleaningoperation.

According to the present invention, there is provided a wafer processingfilm comprising a base film having a Shore D hardness of 40 or less andan adhesive layer disposed on one surface of the base film.

Moreover, it is preferable that an supporting film having a Shore Dhardness greater than 40 be laminated to the surface of the base filmhaving no adhesive layer disposed thereon.

Furthermore, it is also preferable that the adhesive layer contains oneor more members selected from the group consisting of nonionic surfaceactive agents and ethylene glycol derivatives.

BEST MODE FOR CARRYING OUT THE INVENTION

The wafers to which the wafer processing film of the present inventionis directed include not only silicon wafers but also such other wafersas gallium arsenide, gallium phosphide and germanium. It is especiallyuseful in the processing of silicon wafers of large diameter.

The wafer processing film of the present invention is used in such a waythat a wafer to be subjected to surface grinding is affixed to theadhesive layer of this processing film and its surface is then ground.By using this processing film in the above-described way, the wafer canbe prevented from being broken during surface grinding. Moreover, aftercompletion of the processing, contamination of the wafer surface can beprevented by separating the wafer from the processing film and thensubjecting it to a simple cleaning procedure.

The base film used in the wafer processing film of the present inventionmay be selected from various films consisting of such materials asthermoplastic resins, thermosetting resins, natural rubber and syntheticrubbers, provided that they have a Shore D hardness of 40 or less andpreferably 30 or less. As used herein, Shore D hardness means a valueobtained by measurement with a Shore hardness tester of the D typeaccording to ASTM D-2240. Films having a Shore D hardness greater than40 lack the ability to distribute properly the external forces exertedon the wafer and cannot substantially prevent the breakage of wafersbeing ground.

Typical examples of the material constituting the base film includethermoplastic elastomers such as ethylene-vinyl acetate copolymers,polybutadiene, polyurethenes, non-rigid polyvinyl chloride resin,polyolefins, polyesters, polyamides, etc.; synthetic rubbers such asdiene rubber, nitrile rubber, silicone rubber, acrylic rubber, etc.; andthe like. The thickness of the base film may suitably be determinedaccording to the shape and surface condition of silicon wafers to beprotected, the grinding method, and grinding conditions. However, itshould usually be of the order of 10 to 2000 μm.

The wafer processing film of the present invention may comprise atwo-layer structure composed of a base film and an adhesive layer.However, since the base film is highly flexile, the processing film israther poor in workability when it is affixed to a wafer and separatedfrom the ground wafer. Accordingly, in order to improve its workabilitywithout impairing the ability of the base film to prevent waferbreakage, it is preferable to laminate a supporting film having a ShoreD hardness greater than 40 to the surface of the base film having noadhesive layer disposed thereon.

This supporting film may suitably be selected from various films made ofsuch materials as thermoplastic resins, thermosetting resins, paper orwooden sheet laminated with a synthetic resin, and the like, providedthat they have a Shore D hardness greater than 40. Films having a ShoreD hardness of 40 or cannot improve workability in affixing andseparating the wafer processing film.

Typical examples of the material constituting the supporting filminclude synthetic resins such as polyethylene, polypropylene,polyesters, polyamides,

rigid polyvinyl chloride resin, polyether sulfones, acrylic resins,phenolic resins, etc.; paper impregnated with a phenolic resin;polyethylene-coated paper; and the like.

The thickness of the supporting film may suitably be determineddepending on the machines for affixing the processing film to a waferand removing it from the wafer, and the thickness of the base film.However, it should usually be of the order of 10 to 1000 μm.

The supporting film may be laminated to the base film according to anyof various conventionally known processes. For example, these processesinclude:

(1) the process in which a base film and an supporting film are preparedin advance, an adhesive is applied to one of them, and the film aresuperposed and adhered together;

(2) the process in which two films are simultaneously extruded andadhered by two-layer T-die extrusion or two-layer inflation;

(3) the process in which a film is prepared in advance and another resinis laminated thereto by T-die extrusion or calendering; and the like.

As the adhesive substance constituting the adhesive layer disposed onone surface of the base film, there may be used any of commerciallyavailable, common adhesives such as acrylic adhesives, ester adhesives,urethane adhesives and synthetic rubber adhesives. However, it ispreferable to use an adhesive containing a nonionic surface activeagent. Moreover, it is preferable to form the adhesive layer by addingan ethylene glycol derivative to an aqueous emulsion of an adhesive andapplying this mixture to one surface of the base film. Where theadhesive layer has this composition, any dust which may be transferredfrom the adhesive.substance or adhesive layer to the wafer surface canbe relatively easily washed off and, moreover, the wafer surface can beprotected against corrosion.

Suitable nonionic surface active agents include, for example,polyoxyethylene octyl phenyl ether, alkanol amides, polyoxyethylenenonyl phenyl ether, polyethylene glycol and polyoxyethylene laurylether. Anionic and cationic surface active agents are not preferablebecause they tend to corrode the wafer surface. The content of thenonionic surface active agent should suitably be from 0.01 to 50 partsby weight and more preferably from 0.1 to 10 parts by weight, per 100parts by weight of the adhesive substance.

Suitable ethylene glycol derivatives include, for example, diethyleneglycol monobutyl ether, triethylene glycol monomethyl ether, ethyleneglycol monomethyl ether and diethylene glycol monobutyl ether acetate.The ethylene glycol derivatives should preferably have a boiling pointof 100° C. or above and more preferably 150° C. or above. Ethyleneglycol derivatives having a boiling point lower than 100° C. barelycontribute to the improvement of dust removal by wafer cleaning, becausethey tend to evaporate during application of the adhesive substance andbarely remain in the adhesive layer. The amount of ethylene glycolderivative used may suitably be determined in consideration of theadhesion of the adhesive substance to wafers and its effect on dustremoval from the separated wafer. However, it should usually be from 1to 100 parts by weight and more preferably from 5 to 50 parts by weight,per 100 parts by weight of the aqueous emulsion adhesive (having asolids content of 30 to 60% by weight) used for the formation of theadhesive layer.

The thickness of the adhesive layer may suitably be determined dependingon, for example, the surface condition and shape of silicon wafers to beprocessed and the grinding method. However, it should usually be of theorder of 2 to 200 μm.

As the method of applying the adhesive substance to one surface of thebase film, there may be employed any of various conventionally knowncoating processes such as roll coating, gravure coating, bar coating,dip coating, brushing and spray coating. The adhesive substance may beapplied to the whole surface or to selected surface areas of the basefilm.

Since the wafer processing film of the present invention ischaracterized in that the base film has the property of absorbing theexternal forces exerted on wafers and of distributing them properly, thebreakage of wafers being processed can be prevented by affixing thewafers to the wafer processing film and then grinding their surfaces.Where the wafer processing film has a supporting film laminated thereto,it is excellent in shape retention properties and exhibits very goodworkability in affixing the wafer processing film to a wafer andseparating it from the ground wafer, thus making it possible to producea marked effect in the improvement of productivity. Furthermore, wherethe adhesive layer has a preferred composition as defined above, thewafer processing film has the great advantages that after-treatment suchas cleaning of the wafer separated from the wafer processing film can beeasily carried out and contamination or corrosion of the wafer surfacecan be avoided.

The present invention is further illustrated by the following examples.

EXAMPLE 1

One surface of an ethylene-vinyl acetate copolymer resin film (200 μmthick) having a Shore D hardness of 30 as measured according to ASTMD-2240 was subjected to a corona discharge treatment, coated with theacrylic adhesive "Aromatex" (trademark; manufactured by Mitsui-ToatsuChemicals Co., Ltd.) by means of a roll coater, and then dried at 90° C.to form a silicon wafer processing film having disposed thereon anacrylic adhesive layer of about 50 μm thickness.

Using an automatic affixing machine (manufactured by Disco, Ltd.), apiece of this film was affixed to the front surface of a silicon wafer(6 inches) having integrated circuits formed therein and exhibiting asurface roughness of about 50 μm, and the back surface of the wafer wasground by means of a grinding machine (manufactured by Disco, Ltd.).After grinding, the wafer was separated from the film and then washedwith deionized water. In this manner, a total of 100 wafers having aground back surface were produced. During this process, none of thewafers were broken and the overall working time was about 1 hour.

EXAMPLE 2

The same ethylene-vinyl acetate copolymer resin film as used in Example1 was laminated to a polypropylene film (100 μm thick) having a Shore Dhardness of 80, by means of the acrylic adhesive "Bonron" (trademark;manufactured by Mitsui-Toatsu Chemicals Co., Ltd.). Then, a waferprocessing film was formed by disposing the same adhesive layer as usedin Example 1 on the copolymer resin surface of the resulting film in thesame manner as described in Example 1.

Using this film,a total of 100 silicon wafers Were ground in the samemanner as described in Example 1. During this process, none of thewafers were broken and the overall working time was about 30 minutes.

EXAMPLE 3

A silicon wafer processing film was formed in the same manner asdescribed in Example 1, except that a butadiene rubber sheet (300 μmthick) having a Shore D hardness of 20 was used.

Using this film, a total of 100 silicon wafers were ground in the samemanner as described in Example 1. During this process, none of thewafers were broken and the overall working time was about 1 hour.

EXAMPLE 4

According to the two-layer T-die extrusion method, butadiene rubberhaving a Shore D hardness of 20 and polypropylene having a Shore Dhardness of 80 were simultaneously extruded to form a two-layer film(comprising a butadiene rubber layer of 200 μm thickness and apolypropylene layer of 200 μm thickness). Then, a wafer processing filmwas formed by applying an acrylic adhesive layer of about 30 μmthickness to the butadiene rubber surface of the above film in the samemanner as described in Example 1. This film was used by affixing a piecethereof to the surface of a silicon wafer exhibiting a surface roughnessof about 30 μm. Thus, a total of 100 ground silicon wafers were producedin the same manner as described in Example 1. As a result of grinding,none of the wafers were rejected because of breakage and the entireprocessing work was completed in about 30 minutes.

COMPARATIVE EXAMPLE 1

On the front surface of a silicon wafer of the same type as used inExample 1, the polyisoprene resist ink JSR CIR (trademark; manufacturedby Nippon Synthetic Rubber Co., Ltd.) was cast at about 50° C. andcooled for 2 hours. Thereafter, the back surface of the wafer wasground. Then, the wafer was washed with trichloroethylene heated at 50°C. to remove the resist ink, and then rinsed in deionized water. In thismanner, a total of 100 processed silicon wafers were produced. Duringthis process, 20 wafers were broken and the time required to completethe entire processing work was about 5 hours. Thus, when compared withExample 2, the production rate was about 1/10 and the product yield was80%. Furthermore, the washed wafer surfaces showed evidence ofcontamination with the resist ink.

COMPARATIVE EXAMPLE 2

A low-density polyethylene film (200 μm thick) having a Shore D hardnessof 50 and a polypropylene film (100 μm thick) having a Shore D hardnessof 80 were laminated in the same manner as described in Example 2. Then,a wafer processing film was prepared by applying an acrylic adhesivelayer of about 30 um thickness to the low-density polyethylene surfaceof the resulting film in the same manner as described in Example 1.

Using this film, the back surfaces of 100 silicon wafers were ground inthe same manner as described in Example 4. As a result, 76 wafers wererejected because of breakage.

EXAMPLE 5

Into a flask fitted with a thermometer, a reflux condenser, a droppingfunnel, a nitrogen inlet and a stirrer were charged 115 parts by weightof deionized water and 2 parts by weight of polyoxyethylene nonyl phenylether. After the contents were heated to 70° C. with stirring under anatmosphere of nitrogen, 0.5 part by weight of the azo polymerizationinitiator "ACVA" (trademark; manufactured by Otsuka Pharmaceutical Co.,Ltd.) was added thereto and dissolved therein. Then, a monomer mixtureconsisting of 23 parts by weight of methyl methacrylate, 73 parts byweight of 2-ethylhexyl acrylate, 2 parts by weight of glycidylmethacrylate and 2 parts by weight of methacrylic acid was continuouslyadded dropwise thereto over a period of 4 hours. After completion of theaddition, the stirring was continued for an additional 3 hours to effectpolymerization. Thus, there was obtained an acrylic emulsion adhesivehaving a solid content of about 47% by weight.

Using this adhesive, a coating fluid having the following compositionwas prepared.

Acrylic emulsion adhesive --100 parts by weight

Diethylene glycol monobutyl --50 parts by weight ether

Polyoxyethyene phenyl ether --5 parts by weight

A wafer processing film was formed in the same manner as described inExample 1, except that the above coating fluid was used.

A piece of the processing film so formed was affixed to a 4-inch siliconwafer and separated therefrom. The wafer was immersed in isopropylalcohol at 50° C. and cleaned by exposure to ultrasonic waves for 10minutes, then immersed in deionized water at ambient temperature andcleaned by exposure to ultrasonic waves for 10 minutes, and finallydried with an infrared heater. The amount of dust attached to thesilicon wafer so cleaned was evaluated by means of a PC-320/LAS 346tester (manufactured by HICA-ROYCO, Inc.). The results thus obtained areshown in Table 1. As can be seen from this table, only a very smallamount of dust was attached to the wafer, indicating that the wafercould be cleaned satisfactorily.

EXAMPLE 6

One surface of a non-rigid polyvinyl chloride film (70 μm thick) formedby calendering and having a Shore D hardness of 35 was coated with acoating fluid having the following composition was prepared from theabove acrylic emulsion adhesive synthesized in Example 5, which wasapplied by means of a roll coater and then dried at 90° C. to form asilicon wafer processing film having an adhesive layer of 10 μmthickness.

Acrylic emulsion adhesive --100 parts by weight

Triethylene glycol monomethyl --50 parts by weight ether

Polyoxyethylene lauryl ether --2 parts by weight

Using this processing film, the amount of dust attached to the cleanedwafer was evaluated in the same manner as described in Example 5. Theresults thus obtained are also shown in Table 1.

EXAMPLE 7

Using a coating fluid prepared by adding 50 parts by weight ofdiethylene glcol monobutyl ether to 100 parts by weight of the acrylicemulsion adhesive synthesized in Example 5, a silicon wafer processingfilm was formed in the same manner as described in Example 1, exceptthat the thickness of the adhesive layer was 10 μm.

Using this processing film, the amount of dust attached to the cleanedwafer was evaluated in the same manner as described in Example 5. Theresults thus obtained are also shown in Table 1.

REFERENCE EXAMPLE

The same monomer composition as used for the preparation of acrylicadhesive in Example 5 was subjected to solution polymerization and theresulting product was dissolved in acetone to prepare an adhesivesolution (having a solid content of 50% by weight). Using a roll coater,this adhesive solution was applied to one surface of the same non-rigidpolyvinyl chloride film as used in Example 6 and then dried at 90° C. toform a silicon wafer processing film having an adhesive layer of 10 μmthickness.

Using this processing film, the amount of dust attached to the washedwafer was evaluated in the same manner as described in Example 5. Theresults thus obtained are also shown in Table 1. In this case, a verylarge amount of dust was attached to the wafer, indicating that thecleaning procedure used in the other examples failed to clean the wafersatisfactorily.

                  TABLE 1                                                         ______________________________________                                               Amount of dust attached to the                                                wafer (number of particles)                                                   0.5 μm                                                                           0.5-2  2-20   20-50 50-100                                                                              100 μm                                     or less                                                                             μm  μm  μm μm or greater                             ______________________________________                                        Example 5                                                                               50      30    10   0     0     0                                    Example 6                                                                               80      60    20   0     0     0                                    Example 7                                                                               100     80    50   0     0     0                                    Reference                                                                              3500    2030   500  100   100   10                                   Example                                                                       ______________________________________                                    

We claim:
 1. A method of grinding the surface of a wafer comprising thefollowing steps:affixing an adhesive layer disposed on one surface of abase film having a Shore D hardness of 40 or less, to a first surface ofa wafer having first and second surfaces; and grinding said secondsurface of said wafer.
 2. A method of grinding the surface of a waferaccording to claim 1, wherein a supporting film having a Shore Dhardness greater than 40 is laminated to the surface of said base film,said supporting film having no adhesive layer disposed thereon.
 3. Amethod of grinding the surface of a wafer according to claim 1, whereinsaid adhesive layer contains an additive wherein said additive isselected from the group consisting of nonionic surface active agents andethylene glycol derivatives.
 4. A method of grinding the surface of awafer according to claim 3, wherein said ethylene glycol derivativeshave a boiling point of 100° C. or above.
 5. A wafer processing filmcomprising a base film having a Shore D hardness of 40 or less and anadhesive layer disposed on one surface of said base film, said base filmbeing selected from the group consisting of ethylene-vinyl acetatecopolymer resin and butadiene rubber.